The use of solid sorption systems in refrigeration is not new, and was first used commercially in the USA in the 1920's. using silica gel and sulphur dioxide. However, the development of CFCs, and the availability of electricity meant that solid sorption refrigeration was abandoned in favour of the vapour compression cycle. Solid sorption systems are generating renewed interest once more, however, as CFCs (and alternatives) are causing increasing environmental concern. The phasing out of CFCs as refrigerants was scheduled for the year 2000 by the Montreal Protocol (1987); Germany requires phase-out by 1995, and the EC by 1997. Other heat transfer media for the vapour compression cycle such as ammonia, hydrocarbons, CO.sub.2 etc have advantages in some circumstances but are not viewed as true alternatives. Adsorption heat pumps are being viewed positively in the fields of heating and air conditioning, and it seems possible that a first commercial use in this current period would be in automotive air conditioning and/or in a residential or commercial space heating and/or cooling market.
For example U.S. Pat. No. 5,325,916 (UOP), discloses a zeolite-coated aluminium heat exchanger tube, and U.S. Pat. No. 4,581,049 (Schiedel) and U.S. Pat. No. 5,054,544 (Zeotech) are similar. here remains a need for improved solid adsorber materials, and for improved systems.
U.S. Pat. No. 4,199,959 (Institute of Gas Technology) teaches an air conditioning apparatus which does not require any heat transfer fluid. Adsorbers for this apparatus are disclosed comprising aluminium honeycombs bonded to aluminium sheet. To the extent that the teaching of this document can be understood, the physical form of the adsorbers differs from that taught in the present invention in that it appears that the coating is applied to honeycomb structures whose axis is perpendicular to the gas flow. The invention is stated to be principally for low capacity air conditioning, using solar heat for example, that may be used in domestic buildings. We do not believe that this system could readily be adapted for use on board a vehicle.
The present invention provides an improved heat pump adsorber unit, comprising a heat transfer monolith having a plurality of elongated open cells capable of through-flow of gas or vapour, said cells being coated internally with an adsorbent for a refrigerant fluid, and one or more walls defining a passage for a heat exchange fluid, external to said monolith and separated therefrom, the monolith having an effective thermal conductivity from its geometric centre to said passage of at least 5 W/mK.